迭代器模式(iterator pattern) 详细解释

本文地址: http://blog.csdn.net/caroline_wendy

迭代器模式(iterator pattern) : 提供一种方法顺序訪问一个聚合对象中的各个元素, 而又不暴露其内部的表示;

建立迭代器接口(iterator interface), 包括hasNext()方法和next()方法;

不同聚合对象的详细的迭代器(concrete iterator), 继承(implements)迭代器接口(iterator interface), 实现hasNext()方法和next()方法;

详细聚合对象(concrete aggregate), 提供创建迭代器的方法(createIterator).

通过调用聚合对象的迭代器, 就可以使用迭代器, 统一输出接口.

面向对象设计原则:

一个类应该仅仅有一个引起变化的原因.

即一个类应该仅仅有一个责任, 即高内聚.

详细方法:

1. 菜单项, ArrayList和数组的基本元素.

/*** @time 2014年6月20日*/
package iterator;/*** @author C.L.Wang**/
public class MenuItem {String name;String description;boolean vegetarian; //是否是素食double price;/*** */public MenuItem(String name, String description, boolean vegetarian, double price) {// TODO Auto-generated constructor stubthis.name = name;this.description = description;this.vegetarian = vegetarian;this.price = price;}public String getName() {return name;}public String getDescription() {return description;}public double getPrice() {return price;}public boolean isVegetarian() {return vegetarian;}}

2. 详细的聚合对象(concrete aggregate), 包括创建迭代器的方法(createIterator).

/*** @time 2014年6月26日*/
package iterator;/*** @author C.L.Wang**/
public class DinerMenu {static final int MAX_ITEMS = 6;int numberOfItems = 0;MenuItem[] menuItems;/*** */public DinerMenu() {// TODO Auto-generated constructor stubmenuItems = new MenuItem[MAX_ITEMS];addItem("Vegetarian BLT", "(Fakin') Bacon with lettuce & tomato on whole wheat", true, 2.99);addItem("BLT", "Bacon with lettuce & tomato on the whole wheat", false, 2.99);addItem("Soup of the day", "Soup of the day, with a side of potato salad", false, 3.29);addItem("Hotdog", "A hot dog, with saurkraut, relish, onions, topped with cheese", false, 3.05);}public void addItem(String name, String description,boolean vegetarian, double price) {MenuItem menuItem = new MenuItem(name, description, vegetarian, price);if (numberOfItems >= MAX_ITEMS) {System.err.println("Sorry, menu is full! Can't add item to menu");} else {menuItems[numberOfItems] = menuItem;++numberOfItems;}}public Iterator createIterator() {return new DinerMenuIterator(menuItems);}}/*** @time 2014年6月20日*/
package iterator;import java.util.ArrayList;/*** @author C.L.Wang**/
public class PancakeHouseMenu {ArrayList<MenuItem> menuItems;/*** */public PancakeHouseMenu() {// TODO Auto-generated constructor stubmenuItems = new ArrayList<MenuItem>();addItem("K&B's Pancake Breakfast", "Pancakes with scrambled eggs, and toast", true, 2.99);addItem("Regular Pancake Breakfast", "Pancakes with fried eggs, sausage", false, 2.99);addItem("Blueberry Pancakes", "Pancakes made with fresh blueberries", true, 3.49);addItem("Waffles","Waffles, with your choice of blueberries or strawberries", true, 3.59);}public void addItem(String name, String description,boolean vegetarian, double price) {MenuItem menuItem = new MenuItem(name, description, vegetarian, price);menuItems.add(menuItem);}public Iterator createIterator() {return new PancakeHouseMenuIterator(menuItems);}}

3. 迭代器接口(iterator interface), 包括hasNext()方法和next()方法.

/*** @time 2014年6月27日*/
package iterator;/*** @author C.L.Wang**/
public interface Iterator {boolean hasNext();Object next();}

4. 聚合对象的详细的迭代器(concrete iterator), 继承(implements)迭代器接口(iterator interface), 实现hasNext()方法和next()方法;

/*** @time 2014年6月27日*/
package iterator;/*** @author C.L.Wang**/
public class DinerMenuIterator implements Iterator {MenuItem[] items;int position = 0;/*** */public DinerMenuIterator(MenuItem[] items) {// TODO Auto-generated constructor stubthis.items = items;}/* (non-Javadoc)* @see iterator.Iterator#hasNext()*/@Overridepublic boolean hasNext() {// TODO Auto-generated method stubif (position >= items.length || items[position] == null) {return false;}return true;}/* (non-Javadoc)* @see iterator.Iterator#next()*/@Overridepublic Object next() {// TODO Auto-generated method stubMenuItem menuItem = items[position];++position;return menuItem;}}/*** @time 2014年6月27日*/
package iterator;import java.util.ArrayList;/*** @author C.L.Wang**/
public class PancakeHouseMenuIterator implements Iterator {ArrayList<MenuItem> menuItems;int position;/*** */public PancakeHouseMenuIterator(ArrayList<MenuItem> menuItems) {// TODO Auto-generated constructor stubthis.menuItems = menuItems;}/* (non-Javadoc)* @see iterator.Iterator#hasNext()*/@Overridepublic boolean hasNext() {// TODO Auto-generated method stubif (position >= menuItems.size() || menuItems.get(position) == null) {return false;}return true;}/* (non-Javadoc)* @see iterator.Iterator#next()*/@Overridepublic Object next() {// TODO Auto-generated method stubMenuItem menuItem = menuItems.get(position);++position;return menuItem;}}

5. 客户类使用详细聚合类(concrete aggregate)的迭代器(iterator).

/*** @time 2014年6月27日*/
package iterator;/*** @author C.L.Wang**/
public class Waitress {PancakeHouseMenu pancakeHouseMenu;DinerMenu dinerMenu;/*** */public Waitress(PancakeHouseMenu pancakeHouseMenu, DinerMenu dinerMenu) {// TODO Auto-generated constructor stubthis.pancakeHouseMenu = pancakeHouseMenu;this.dinerMenu = dinerMenu;}public void printMenu() {Iterator pancakeIterator = pancakeHouseMenu.createIterator();Iterator dinerIterator = dinerMenu.createIterator();System.out.println("MENU\n----\nBREAKFAST");printMenu(pancakeIterator);System.out.println("\nLUNCH");printMenu(dinerIterator);}private void printMenu(Iterator iterator) {while (iterator.hasNext()) {MenuItem menuItem = (MenuItem)iterator.next();System.out.print(menuItem.getName() + ": ");System.out.print(menuItem.getPrice() + " -- ");System.out.println(menuItem.getDescription());}}}

6. 測试代码:

/*** @time 2014年6月27日*/
package iterator;/*** @author C.L.Wang**/
public class MenuTestDrive {/*** @param args*/public static void main(String[] args) {// TODO Auto-generated method stubPancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();DinerMenu dinerMenu = new DinerMenu();Waitress waitress = new Waitress(pancakeHouseMenu, dinerMenu);waitress.printMenu();}}

7. 输出:

MENU
----
BREAKFAST
K&B's Pancake Breakfast: 2.99 -- Pancakes with scrambled eggs, and toast
Regular Pancake Breakfast: 2.99 -- Pancakes with fried eggs, sausage
Blueberry Pancakes: 3.49 -- Pancakes made with fresh blueberries
Waffles: 3.59 -- Waffles, with your choice of blueberries or strawberriesLUNCH
Vegetarian BLT: 2.99 -- (Fakin') Bacon with lettuce & tomato on whole wheat
BLT: 2.99 -- Bacon with lettuce & tomato on the whole wheat
Soup of the day: 3.29 -- Soup of the day, with a side of potato salad
Hotdog: 3.05 -- A hot dog, with saurkraut, relish, onions, topped with cheese